Apparatus for controlling and metering fluid flow

ABSTRACT

A device for metering and controlling fluid flow includes a variable orifice and is configured to use a pressure sensor. The device includes a fluid flow conduit having at least one planar inner wall that extends along a portion of the fluid flow conduit length, and an element having a linear edge configured to mate with the at least one planar inner wall of the fluid flow conduit. The element is movable in a direction transverse to an axis of the conduit between an open position wherein fluid flows through the conduit and a closed position wherein the element substantially shuts off fluid flow in the conduit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 60/500,774, filed on Sep. 4, 2003, entitled APPARATUS FORCONTROLLING AND METERING FLUID FLOW, the disclosure of which isincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention generally relates to fluid flow, and moreparticularly to a variable orifice for metering and controlling fluidflow.

2. Related Art

In process control industries, it is common to use small diameter tubesto carry process fluids at low flow rates when small amounts of fluidsare required for manufacturing processes. The tubes are almost always ofa circular cross-section. Instruments used to measure a flow rate in thetubes must interface with a fluid flowing in the tube while minimizingdisturbance to the fluid flow. To minimize disturbance to the fluidflow, the instrument typically includes a circular cross-section tomatch the cross-section of the tubes. The flow rate for a flow metermeasuring a change in pressure across an orifice is defined by thefollowing equation:

$Q = {C*A_{0}*\left( \frac{1}{1 - \left( \frac{A_{0}}{A_{P}} \right)^{2}} \right)^{\frac{1}{2}}*\left( {2*\frac{\left( {P_{hi} - P_{lo}} \right)}{\rho}} \right)^{\frac{1}{2}}}$

Where:

-   -   Q=volumetric flow rate    -   C=orifice discharge coefficient    -   A_(o)=cross-sectional area of the orifice    -   A_(p)=cross-sectional area of the pipe    -   P_(hi)=upstream pressure    -   P_(lo)=downstream pressure    -   ρ=density of the fluid

Flow meters used for measuring flow rates in small tubes may have thepressure sensors and orifice integrated in the same housing. Since theflow rate is a function of the cross-sectional area of the orifice, itis important to know with precision the size of the orifice opening.Typically, orifice based flow meters include an orifice having a fixedopening and the user is required to change the entire flow meter inorder to obtain a different orifice size to accommodate different flowrates. Attempts have been made to produce flow meters with variableorifices. However, if the orifice opening does not retain a consistentshape as the size of the orifice opening is changed, errors result whencalculating the flow rate using the above flow equation. For example, ifa circular orifice compresses into a slightly elliptical shape ratherthan a perfect circular shape, an error may result when calculating theflow rate because the area value for the equation assumes the shape willremain circular. Also, the shape of the front edge and the rear edge ofthe orifice directly affect the discharge coefficient of the orifice andsubsequent flow characteristics of the orifice. If the shape of thefront edge or rear edge of the orifice changes with the size of theopening, flow characteristics of the orifice will change continuously.If the discharge coefficient is not consistent as the size of theorifice opening changes, and if it is not known with precision, errorswill again result using the above flow equation.

Metering and controlling fluid flow is most commonly performed usingseparate devices or at least separate features included in a singledevice. For example, a device that meters fluid flow using an orificemay include a separate valve member that controls the amount andpressure of fluid flowing through the flow tubes, and therefore theorifice. In other applications, a separate valve device is positioned inthe flow path before or after the metering device. In either scenario,the separate nature of the metering and controlling functions results ina bulky and often expensive arrangement for performing both metering andcontrol of the fluid flow. Also, because the separate features must beconnected together, additional seals or gaskets are required to preventleaks.

Known variable orifice devices are ineffective for several reasons.First, known variable orifice devices typically use circular or curvedmembers that are moved with respect to the fluid flow to change the sizeof the orifice. Because of the curved nature of these members, the shapeof the orifice changes as the size of the orifice changes, which resultsin significant errors when calculating the fluid flow over a range oforifice sizes. Second, the changed shape of the orifice leads tonon-ideal orifice shapes for at least a portion of the flow range. Thisleads to inconsistent flow characteristics for any given opening as flowrate changes, again leading to errors in the calculation of fluid flow.

A flow device that addresses these and other shortcomings of known flowcontrol and metering devices would be an important advance in the art.

SUMMARY OF THE INVENTION

The present invention relates to a device for metering and controllingfluid flow that includes a variable orifice and a pressure sensor. Inone aspect of the invention, the device includes a fluid flow conduithaving at least one planar inner wall that extends, and an elementhaving a linear edge configured to mate with the at least one planarinner wall of the fluid flow conduit. The element is movable in adirection transverse to an axis of the conduit between an open positionwherein fluid flows through the conduit, and a closed position whereinthe element substantially shuts off fluid flow in the conduit.

Another aspect of the invention relates to a device for controllingfluid flow or for metering fluid flow, of the type having a variableorifice and configured to use a pressure or differential pressuresignal. The device includes a conduit having first, second and thirdsegments, wherein the first and third segments have a circularcross-section and the second segment includes a non-circularcross-section having at least two planar portions and is positionedbetween the first and third segments. The device also includes anelement having at least one linear edge configured to engage the secondsegment to substantially shut off fluid flow in the conduit.

A further aspect of the invention relates to a device for measuring andcontrolling fluid flow that includes a conduit having an input portionwith an inner circular cross-section, and an orifice portion with aninner rectangular cross-section, a pressure sensor configured to measurepressure within the conduit, and a movable element adapted andconfigured to engage the inner rectangular cross-section of the orificeportion to control fluid flow.

Another aspect of the invention relates to an apparatus for controllingand metering fluid flow that includes a housing, a movable element, andfirst and second pressure sensors. The housing includes a fluid flowconduit having first, second and third portions along a length of theconduit, the second portion including at least one planar sidewall, andalso includes an element bore providing access to the conduit. Thehousing further includes first and second sensor chambers that are influid communication with respective first and second portions and secondand third portions of the conduit. The element includes a linear edgeconfigured to mate with the at least one flat sidewall of the conduitsecond portion to form a seal therewith and is movable in the elementbore between an open position wherein fluid flows through the conduitand a closed position wherein the element seats against the planarsidewall and substantially shuts off fluid flow in the conduit. Thefirst and second pressure sensors are mounted in respective first andsecond sensor chambers and are configured to determine a pressuredifferential across the conduit.

Another aspect of the invention relates to a method of controlling fluidflow through a device that includes at least one pressure sensor, aconduit having a first portion with a circular inner cross-section and asecond portion with a rectangular inner cross-section, and a movableelement having at least one linear edge. The method includes moving themovable element into the conduit in a direction transverse to alongitudinal direction along a length of the conduit, and engaging thelinear edge of the movable element with the at least one flat sidewallof the conduit when in the closed position to form a seal by seatingwith the at least one flat sidewall.

A further aspect of the invention relates to a method of metering andcontrolling fluid flow through a fluid flow apparatus that includes ahousing, a movable element, and first and second pressure sensors. Themethod includes forming a conduit through the housing that includes atleast first, second and third portions. The first and third portionsinclude a circular inner cross-section and the second portion includesat least one planar sidewall. The method also includes forming first andsecond sensor chamber in the housing so as to be in fluid communicationwith respective first and second portions of the conduit and second andthird portions of the conduit. The method further includes forming aelement bore in the housing that extending transverse to the conduit andprovides access to the second portion of the conduit, moving the movableelement in the element bore to control fluid flow in the conduit, andengaging the linear edge of the movable element with the at least oneflat sidewall of the conduit when in the closed position to form a sealwith the at least one planar sidewall. The method also includesdetermining a pressure differential between the first and second sensorchambers using a pressure signal provided by each of the first andsecond pressure sensors, and metering the fluid flow based on thepressure differential. Alternatively, a single differential pressuresensor may be used in place of separate sensors. Another aspect of themethod may include using a pressure signal from an outside source forcontrolling and metering fluid flow in the device in place of or inaddition to pressure signals from the pressure sensor(s) associated withthe device.

These and further objects of the present invention will become clearerin light of the following detailed description of illustrativeembodiments of this invention described in connection with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The illustrative embodiments may best be described by reference to theaccompanying drawings where:

FIG. 1 is a top perspective view of an flow device according toprinciples of the invention;

FIG. 2 is a top plan view of the flow device shown in FIG. 1;

FIG. 3 is a cross-sectional view of one example configuration of theflow device shown in FIG. 2 taken along cross-sectional indicators 3—3;

FIG. 4 is a cross-sectional view of the example flow device shown inFIG. 3 taken along cross-sectional indicators 4—4;

FIG. 5 is an enlarged view of the orifice and movable element portion ofthe device shown in FIG. 4;

FIG. 6 is a cross-sectional view of the example flow device shown inFIG. 2 taken along cross-sectional indicators 6—6;

FIG. 7 is a cross-sectional view of the example flow device shown inFIG. 2 taken along cross-sectional indicators 7—7;

FIG. 8 is a cross-sectional view of the example flow device shown inFIG. 2 taken along cross-sectional indicators 8—8;

FIG. 9 is a cross-sectional view of another example configuration of theflow device taken along a length of the flow device; and

FIG. 10 is a cross-sectional view of the example flow device shown inFIG. 9 taken along cross-sectional indicators 10—10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention generally relates to metering and controlling fluid flow,and more particularly to a variable orifice for metering and controllingfluid flow. The variable orifice may be part of a flow device thattranslates an incoming flow having a circular cross-sectional flow areato a metered flow having a non-circular cross-sectional flow area thatincludes at least one linear, flat side. One example cross-sectionalshape for the metered flow is a rectangle having four linear, flatsides. Other cross-sectional shapes for the metered flow may include,for example, a parallelogram, a rhombus, or other polygon shape, but mayalso include shapes that have a combination of flat and curved surfaces.The variable orifice may be particularly suited for use in adifferential pressure flow meter as will be described herein withreference to the several drawings, although such an application is onlyexemplary of the many applications to which principles of the presentinvention may be applied.

One example flow device 10 for controlling and metering fluid flow isshown in FIGS. 1–8. The device includes a housing 12, a moveable element14, first and second pressure sensors 16, 18, and inlet and outletconduit connectors 22, 20. A conduit 30 is formed through the housingand includes first, second and third segments 50, 52, 54. The housingalso includes first and second sensor bores 36, 38 that intersect withthe conduit 30 in a direction transverse to the conduit 30, and anelement bore 40 that also intersects with conduit 30 in a directiontransverse to conduit 30. In this example, element bore 40 and sensorbores 36, 38 extend parallel to each other, but may be alignedperpendicular to each other in other embodiments, such as flow device100 shown in FIGS. 9 and 10. Housing 12 may also be divided intoseparate pieces or halves 13, 15 (see FIG. 1) to facilitate preciseformation of intricate features within the housing.

Moveable element 14 includes a base 42 and a contact member 44, and ispositioned in element bore 40 so as to extend into second segment 52 ofthe conduit 30. Contact member 44 includes a leading edge 46, a taperedtrailing edge 48, and a planar contact surface 49 (see FIG. 5)configured to mate with a planar surface (for example, fixed wall 90described below and shown in FIG. 5) of second segment 52. The movableelement 14 is moveably adjustable along a linear axis through a range ofpositions between an open (retracted) position and a closed position,with movement of the movable element 14 being limited to the linearaxis. The open position allows a maximum fluid flow through the conduit30. The fluid flow through the conduit 30 decreases as the movableelement 14 is moved toward the closed position due to contact with thefluid. Adjustment of the movable element 14 in element bore 40 may beperformed using, for example, a linear actuator, a stepper motor, ahydraulic or pneumatic actuator, a solenoid, a servo motor, or a manualdevice such as a threaded shaft with a thumb turn button. The positionof the movable element 14 may be determined using, for example, a Halleffect sensor, magnetostrictive devices, linear variable differentialtransformers (LVDTs), optical encoder, and other position determiningtechnologies. Limiting movement of element 14 to linear motion withinelement bore 40 may simplify positioning of movable element 14.

Second segment 52 includes an inlet portion 60, an outlet portion 62,and an orifice portion 64 positioned between the inlet and outletportions 60, 62. The inlet portion 60 is in fluid communication withsensor chamber 32 at one end, and includes a plurality of taperedsurfaces at a second end adjacent to the orifice portion 64. Similarly,outlet portion 62 is in fluid communication with sensor chamber 34 atone end, and includes a plurality of tapered surfaces at an opposing endadjacent to orifice portion 64.

The inlet and outlet portions of the orifice segment of the devicepreferably include a plurality of fixed sidewalls that define anoncircular cross-section. The example first and third portions 60, 62include four fixed walls substantially in the shape of a square (seeexample cross-section of inlet portion 60 in FIG. 7). As used throughoutthis document, rectangular is defined as a four-walled shape and asquare is defined as a rectangle that has four walls of the same length.The walls of a rectangle are substantially flat or linear and theintersection of two walls provides an angle of about 90°. In someapplications, the corners of the rectangle may be tapered slightly witha round, fillet, chamfer or like feature as a result of manufacturinglimitations. Further, a portion of one or more of the walls may beslanted or chamfered slightly to create sealing points or to meet otherdesign goals and/or address manufacturing limitations. In embodimentsthat include a combination of linear and curved walls (not shown), theintersection of these walls may also include features such as rounds,fillets, chamfers, etc. Finally, a portion of one or more of the wallsmay be formed by the exposed face of a gasket or seal.

Tapers 70, 72, 74, 76 are formed in the sidewalls of inlet portion 60 toreduce the cross-sectional area at the point where inlet portion 60abuts to orifice portion 64. The tapers 70, 72, 74, 76 are aligned at asingle axial position so as to create a reduction in cross-sectionalarea of portion 60 in a single step (see FIG. 3–5). Outlet portion 62also includes a square shaped cross-section with tapered surfaces 78, 80(see FIG. 4) on opposing sidewalls so as to reduce the cross-sectionalarea of outlet portion 62 at the transition point between orificeportion 64 and outlet portion 62.

Orifice portion 64 includes three fixed walls 90, 92, 94 with fixed wall90 including a tapered trailing edge 96 and a leading edge 98 (see FIG.5). As a result, the cross-sectional area of orifice portion 64 tapersout to the larger cross-sectional area of portion 62 in two steps withsets of tapers 96, 48 and 78, 80. As shown in the cross-sectional viewof FIG. 8, orifice portion 64 has a relatively small cross-sectionalarea as compared to the cross-sectional area of inlet portion 60 shownin FIG. 7.

The leading edges 46, 98 and trailing edges 96, 48 of respective movingelement 44 in orifice portion 64 provide consistent flow characteristicsinto and out of the orifice portion 64. A cross-sectional size of theorifice portion 64 is determined by the location of the movable element14 in relation to the fixed walls 90, 92, 94 of the orifice portion 64.The orifice portion 64 is void of sensor openings and dead volume spacesto avoid disruptions to the fluid flow and potential accumulation ofprocess material or sediment.

A linear actuator (not shown) such as those discussed above (e.g.,stepper motor, servo motor, etc.) may be used to affect movement of themovable element 14. By moving along a single linear axis, the movableelement 14 linearly changes the cross-sectional size of the orificeportion 64 while maintaining a generally uniform shape to provide arelatively consistent set of flow characteristics through the range ofmovable element positions. The cross-sectional shape of orifice portion64 allows repeatable regulation of the fluid flow in accordance with theposition in the range of positions of the movable element 14. In oneexample wherein the uniform shape is a rectangle, the height of thecross-sectional area of the orifice portion 64 is reduced in size as themovable element 14 moves between the open and closed positions.Maintaining a rectangular shape, or at least a shape having at least oneplanar or linear sidewall, minimizes variations in flow characteristics(variable “C” in the flow rate equation in the Background section), thusreducing errors when determining the flow rate for each orifice size.

In another example flow device 100 shown in FIGS. 9 and 10, the flowdevice includes a housing 112, a moveable element 114, first and secondpressure sensors 116, 118, inlet and outlet conduit connectors 120, 122,and a conduit 130 formed in the housing. The housing also includes firstand second sensor chambers 132, 134, sensor bores 136, 138 that housefirst and second pressure sensors 116, 118, and an element bore 140 thathouses moveable element 114. The conduit includes first, second andthird segments 150, 152, 154, wherein the first and third segments 150,154 include a circular cross-section and the second segment 152 includesa noncircular cross-section.

The second segment 152 includes an inlet portion 160, an outlet portion162, and an orifice portion 164. Orifice portion 164 includes first,second and third fixed walls 190, 192, 194, a tapered trailing edge 196,and a tapered leading edge 198.

The inlet and outlet portions 160, 162 each include two sets of opposedsidewalls that are tapered at separate axial positions adjacent toorifice portion 164. Inlet portion 160 includes tapered surfaces 170,172 at a first axial position. The cross-sectional area of secondsegment 152 is further reduced at the inlet side of orifice portion 164with tapered leading edge 198 and tapered leading edge 146 of movableelement 114. The cross-sectional area of second segment 152 is expandedout at the outlet side of orifice portion 164 with tapered trailing edge196 and tapered trailing edge 148 of movable element 114. Outlet portion162 includes tapered surfaces 178, 180 on a first set of opposedsidewalls to further expand out the cross-sectional area of segment 152after the orifice portion 164. Thus, flow device 100 differs from flowdevice 10 in that the tapered surfaces of the inlet portion 160 isspaced apart axially along conduit 130 rather than a simultaneous taperof all four sidewalls at the inlet side of the orifice portion as shownwith reference to flow device 10 in FIGS. 3–5.

Another difference between flow devices 10 and 100 is the entrance intoorifice portions 64, 164. In flow device 10, the tapers 70, 72, 74, 76do not directly taper the fluid into the orifice portion 64. As bestseen in FIG. 5, the leading edge 46 of moveable element 14 and theleading edge 98 of orifice portion 64 provide a generally flat wall-likesurface that creates a high pressure area at the inlet of the orificeportion 64. Depending on the position of moveable element 14 along thedirection A, the pressure at the inlet to orifice portion 64 may changesomewhat, which is to be expected when increasing or decreasing the sizeof the orifice portion 64. The pressure at the inlet to orifice portion64 may also be affected by the size of the wall-like structure definedby the leading edges 46, 98.

In contrast, the entrance to orifice portion 164 and flow device 100more directly tapers the inlet portion 60 into the orifice portion 64due to the tapered leading edge 148 of moving element 114 and the moresignificant tapers 170, 172.

In use, fluid first enters flow device 10 (which example will be usedfor the remainder of the description of various aspects of theinvention) through first segment 50 of conduit 30. The flow throughsegment 50 has flow characteristics that match the circularcross-section of first segment 50. The flow then enters the open sensorchamber 32 where a transition volume is provided prior to the fluid flowentering the non-circular inlet portion 60 of second segment 52. Theflow is then reduced in cross-sectional area by the several tapersformed in inlet portion 60 just before orifice portion 64. As mentionedabove, a higher pressure is generated at the inlet to orifice portion 64due to the very small cross-sectional area of orifice portion 64 and thewall-like structure created by leading edges 46, 98. The cross-sectionalarea of orifice portion 64 is dependent on the position of moveableelement 14 in the direction A. Each position along the direction Acorresponds to a different cross-sectional area of the orifice portion64 for use in determining the volumetric flow through the flow device10.

As the fluid exits orifice portion 64, the cross-sectional area of thefluid flow increases due to tapers 78 and 80 and trailing edges 48 and96 of the moveable element 14 and orifice portion 64 as the flow entersportion 62. The cross-sectional area of outlet portion 62 preferably hasthe same size and shape as the cross-section of inlet portion 60 (whichis a square cross-section in the example flow device in flow device10—see FIG. 10). Flow exiting outlet portion 62 enters sensor chamber 34where another transition volume is provided before the fluid flow entersthe third segment 54 and takes on a flow pattern for the circularcross-section of third segment 54.

The first and second pressure sensors 16, 18 are positioned at opposingsides of orifice portion 64 so as to be able to determine a differencein pressure at the inlet and outlet sides of second segment 52 ofconduit 30. The first and second pressure sensors 16, 18 may be mountedproximate the process liquid to minimize the amount of dead volume ofthe fluid and reduce crystallization and particle buildup between thefirst and second pressure sensors 16, 18 and the fluid in conduit 30. Inother aspects of the present invention, a single differential pressuresensor may be used to communicate with both the first and second sensorchambers 32, 34 to determine the pressure difference. Furthermore, onlya single pressure sensor may be required in applications where one ofthe first or second sensor chamber 32, 34 has a fixed pressure. Forexample, if the second sensor chamber 34 is downstream of the orificeand empties into an open tank at atmospheric pressure, a downstreampressure measurement is not required and the pressure measurement fromthe first sensor 16 may be used singly with atmospheric pressure todetermine the pressure differential. Likewise, if the first sensorchamber 32 is upstream of the orifice portion 64 and is accepting liquidfrom a pressurized tank where pressure is tightly controlled to a fixedvalue, an upstream pressure is not required and the pressure measurementfrom the second sensor 18 may be used singly with the fixed upstreampressure value to determine the pressure differential.

Other example embodiments may use a single differential pressure sensorthat takes pressure readings from the inlet and outlet sides of theorifice portion of the device and determines a differential pressureacross the orifice portion. This and other types of sensors do notnecessarily have to be mounted in a sensor bore, nor does the sensorbore being used require a larger cross-sectional area than thecross-sectional area of the conduit. For example, a sensor may beconfigured to obtain pressure readings using a small probe that requiresa very small entrance opening into the conduit relative to the conduitsize, and the sensor can be mounted at a different location within oradjacent to the device housing.

Yet further embodiments may not include any sensors associated directlywith the device, but may be configured to use pressure signals providedby outside sources. Such pressure readings from an outside source mayinclude, for example, a pressure reading from a pressure sensorpositioned up or down stream from the device, or a pressure signalrepresentative of a know static pressure condition for the system eitherup or down stream of the device. Thus, although the device does notrequire a pressure sensor, the device is preferable configured to use apressure signal for purposes of metering and controlling fluid flowingthrough the device.

A pressure signal representing a pressure differential across an orificemay be used with the cross-sectional area of the orifice, thecross-sectional area of the inlet and outlet portions just before andafter the orifice, and the density of the fluid to determine thevolumetric flow rate (discussed in the Background section above).

The sensor chambers discussed herein may have a size and volume that isdependent on the size of the sensor housed in the sensor bore. A largesensor bore (such as bore 36 shown in FIG. 3) may advantageously providea large sensor chamber that effectively transitions flow and pressurebetween the circular and non-circular segments of the device conduit. Inother embodiments that do not include a sensor chamber or include asensor chamber that is very small relative to the size of the conduit,the device may include other transition features suited for use in thoseconfigurations.

Various materials may be well suited for use with a flow deviceaccording to principles of the present invention. In one example, themovable element is formed from a rigid material such as, for example,metal, metal alloys such as stainless steel, polymer materials such asTeflon and other rigid plastics, ceramics, or industrial gemstones.Likewise, the housing and other features of the example flow devices maybe made of similar metallic, polymer, ceramic or other types ofcorrosive or non-corrosive materials.

Flow device 10 is symmetrical about the conduit 30 and along a length ofthe housing 12. As will be recognized by those skilled in the art, aflow device according to principles of the present invention may benonsymmetrical in various respects without departing from the spirit orscope of the present invention.

Flow device 10 includes several features in combination believed toproduce synergistic results. Such features may be utilized singly and inother combinations with other features according to the teachings of thepresent invention. For example, according to the teachings of thepresent invention, the movable element 14 may be used to control fluidflow without metering the flow. Likewise, the orifice portion 64 may beused without the movable element 14 and in combination with otherfeatures of the device, such as the first and second sensor chambers 30,32 and the first and second pressure sensors 16, 18 to provide meteringof the fluid flow without controlling the flow. Such a feature may beuseful if a fixed pressure signal (ΔP) is desired and the device maythen be used for metering only.

Another advantage of the present invention is that the pressure signal(ΔP) may be optimized at each flow rate by varying the orifice size. Forexample, the pressure signal may be set at a minimum value for a givenflow rate by varying the orifice size. Furthermore, the pressure signalmay be optimized for every desired flow rate and inlet pressureavailable by varying the orifice size.

Furthermore, although the cross-sections of the inlet, outlet andorifice portions 60, 62, 64 of second segment 52 are shown having arectangular shape, it may be appreciated that the cross-sections may becross-sections of different shapes, such as, but not limited to,rectangles, isosceles triangles or the like. Furthermore, differentportions of the second segment 52 may have dissimilar cross-sectionalshapes and sizes, and may have varying shapes or sizes along a length ofeach portion of the second segment 52. Additionally, although theorifice portion 64 has a rectangular cross-sectional, the leading andtrailing portions of the orifice portion 64 defined by the leading andtrailing edges 44, 46 of the movable element 14 and the leading andtrailing edges 98, 96 of the fixed walls 90, 92, 94 may be of differentsizes, shapes and orientations than those shown in the figures.

The above specification, examples and data provide a completedescription of the manufacture and use of the composition of theinvention. Since many embodiments of the invention may be made withoutdeparting from the spirit and scope of the invention, the inventionresides in the claims hereinafter appended.

1. A device for controlling fluid flow, of the type having a variableorifice and configured to use a pressure signal, comprising: a fluidflow conduit having a circular cross section; an orifice defined along alength of the conduit, the orifice having at least one planar wallextending in a longitudinal direction of the conduit and defining amaximum cross sectional area that is less than half a cross-sectionalarea of the conduit; and an element having a linear edge configured tomate with the at least one planar wall of the orifice to form a sealtherewith, the element being movable in a direction transverse to thelongitudinal direction between an open position wherein fluid flowsthrough the orifice and a closed position wherein the elementsubstantially shuts off fluid flow through the orifice.
 2. The device ofclaim 1, wherein the orifice cross-section is defined in part by aposition of the element between the open and closed positions.
 3. Thedevice of claim 1, wherein the orifice includes at least one contouredsidewall and the element includes at least one edge having a curvaturethat substantially matches the cross-sectional shape of the contouredsidewall of the orifice.
 4. The device of claim 1, wherein the pressuresignal is provided by a pressure sensor mounted in the housing.
 5. Thedevice of claim 1, wherein the pressure signal is provided by a pressuredevice mounted outside the housing either upstream or downstream of thedevice.
 6. A device for measuring fluid flow, of the type having avariable orifice and configured to use a pressure signal, comprising: afluid flow conduit having a planar inner wall extending in alongitudinal direction of the conduit; and an element having a generallyrectangular shaped surface facing the planar inner wall and configuredto mate with the planar inner wall to form a seal therewith, therectangular shaped surface having a length dimension in the longitudinaldirection that is at least as great as a width dimension of therectangular shaped surface, the element being movable in a directiontransverse to the longitudinal direction between an open positionwherein fluid flows through the conduit and a closed position whereinthe element substantially shuts off fluid flow in the conduit.
 7. Thedevice of claim 6, wherein the conduit includes a rectangularcross-section defined in part by the planar inner wall, a circularcross-section upstream and downstream of the planner inner wall, andtapers that transition from the circular cross-section to therectangular cross-section upstream and downstream of the planar innerwall.
 8. The device of claim 6, wherein the rectangular shaped surfaceincludes a leading edge facing upstream to the fluid flow and a trailingedge facing downstream to the fluid flow, wherein at least one of thetrailing edge and the leading edge includes a taper.
 9. The device ofclaim 6, wherein the pressure signal is provided by a pressure sensormounted in the housing.
 10. The device of claim 6, wherein the pressuresignal is provided by a pressure device mounted outside the housingeither upstream or downstream of the device.
 11. A device forcontrolling fluid flow, of the type having a variable orifice and apressure sensor, comprising: a conduit having first, second and thirdsegments, the first and third segments having a circular cross-section,and the second segment having a non-circular cross-section with at leasttwo planar portions and being positioned between the first and thirdsegments, a cross-sectional area of the second segment is less than across-sectional area of the first and third segments; and an elementhaving at least one planar surface facing one of the at least two planarportions of the second segment and configured to engage the secondsegment to substantially shut off fluid flow in the conduit, the planarsurface having a length dimension in a longitudinal direction of theconduit that is at least as great as a width dimension of the planarsurface.
 12. A device for measuring and controlling fluid flow,comprising: a conduit having an input portion with an inner circularcross-section, and an orifice portion with an inner rectangularcross-section, wherein the inner rectangular cross-section defines amaximum area less than an area defined by the inner circularcross-section; a pressure sensor configured to measure pressure withinthe conduit; and a movable element adapted and configured to engage theinner rectangular cross-section of the orifice portion to control fluidflow.
 13. An apparatus for controlling and metering fluid flow,comprising: a housing including: a fluid flow conduit having first,second and third portions along a length of the conduit, the first andthird portions having a circular cross-section, and the second portionincluding at least one planar sidewall and having a maximumcross-sectional area less than a cross-sectional area of the firstportion, the second portion being positioned between the first and thirdportions; an element bore extending transverse to the conduit andproviding access to the second portion; and first and second sensorchambers defined in the housing along the length of the conduit onopposing sides of the second portion and directly exposed to fluidflowing through the conduit; an element having a planar surface arrangedand configured to mate with the at least one planar sidewall to form aseal therewith and movable in the element bore between an open positionwherein fluid flows through the conduit and a closed position whereinthe element substantially shuts off fluid flow through the conduit; andfirst and second pressure sensors mounted in respective first and secondsensor chambers and configured to determine a pressure differential inthe housing.
 14. The apparatus of claim 13, wherein the first and thirdportions of the conduit have a circular cross-section, and the secondportion of the conduit has a rectangular cross-section.
 15. Theapparatus of claim 13, wherein the planar surface has a length dimensionin a longitudinal direction of the conduit that is at least as great asa width dimension of the planar surface.
 16. The apparatus of claim 15,wherein the second portion includes an inlet and an outlet that eachinclude at least one tapered surface that transitions from a largercross-sectional area of the first and third section to the smallercross-sectional area of the second portion.
 17. The apparatus of claim13, wherein the element includes a leading edge facing upstream to thefluid flow and a trailing edge facing downstream to the fluid flow, andat least one of the trailing edge and the leading edge includes a taperthat substantially matches a tapered surface of the second portion. 18.The apparatus of claim 13, wherein the housing is divided into at leastfirst and second portions along a plane that passes through a center ofthe conduit.
 19. The apparatus of claim 13, wherein the first and secondsensor chambers are accessible through respective first and secondsensor bores that extend transverse to the conduit.
 20. The apparatus ofclaim 19, wherein the first and second sensor bores extend in adirection perpendicular to the direction of the element bore.
 21. Amethod of controlling fluid flow through a device that includes apressure sensor, a conduit having a first portion with a circular innercross-section and a second portion with a rectangular innercross-section having a maximum cross-sectional area that is smaller thana cross-sectional area of the first portion, and a movable elementhaving at least one linear edge, the method comprising the steps of:moving the movable element in the conduit in a direction transverse to adirection along a length of the conduit; and engaging the linear edge ofthe movable element with the at least one flat sidewall of the conduitwhen in the closed position to form a seal with the at least one flatsidewall.
 22. The method of claim 21, wherein the device furtherincludes a housing, and the conduit extends through the housing, thehousing including a sensor chamber positioned between and in fluidcommunication with the first and second portions of the conduit, and aelement bore extending transverse to the conduit and providing access tothe second portion of the conduit, and the movable element extendsthrough the element bore.
 23. A method of metering fluid flowing througha device that includes a conduit having a first portion with a circularinner cross-section and a second portion with a rectangular innercross-section, and a movable element having a planar surface facing aplanar sidewall of the second portion, the planar surface having alength dimension in a longitudinal direction of the conduit that is atleast as great as a width dimension of the planar surface, wherein thedevice is configured to use a pressure signal, the method comprising thesteps of: moving the movable element in the conduit in a directiontransverse to a longitudinal direction along a length of the conduit;and engaging the planar surface of the movable element with the planarsidewall of the conduit when in the closed position to form a seal withthe at least one planar sidewall.
 24. The method of claim 23, whereinthe device further includes a housing, and the conduit extends throughthe housing, the housing including a sensor chamber positioned betweenand in fluid communication with the first and second portions of theconduit, and a element bore extending transverse to the conduit andproviding access to the second portion of the conduit, and the movableelement extends through the element bore.
 25. A method of metering andcontrolling fluid flow through a fluid flow apparatus, the fluid flowapparatus including a housing, a movable element, and first and secondpressure sensors, the housing including a conduit, first and secondsensor chambers, and an element bore, the conduit having at least first,second and third portions, the first and third portions having acircular inner cross-section and the second portion including at leastone planar sidewall, the second portion having a maximum cross-sectionalarea less than cross-sectional areas of the first and third portions,the first and second sensor chambers configured to receive the first andsecond pressure sensors, respectively, wherein the first and secondpressure sensors are directly exposed to fluid flowing through theconduit, and the element bore extends transverse to the conduit in thehousing and provides access to the second portion of the conduit, themethod comprising; moving the movable element in the element bore tocontrol fluid flow in the conduit; engaging the movable element with theat least one planar sidewall of the conduit when in the closed positionto form a seal with the at least one planar sidewall; determining apressure differential between the first and second sensor chambers usinga pressure signal provided by each of the first and second pressuresensors; and metering the fluid flow based on the pressure differential.